/* main的四周padding */
.main{
    box-sizing: border-box;
    width: calc(100% - 240px);
    height: calc(100% - 100px);
    background-color: rgba(0, 0, 0, .5  );
    position: absolute;
    right: 20px;
    top: 80px;
    box-shadow:0px 0px 5px 5px #20AAE9;
    border-radius: 5px;
    color: #fff;
    padding: 10px;
}